Ok so if it ain't the cap plugged I will tear the cylinder apart and reseal it. Change fluid and filter and ad some lucas,just as a precaution. Thanks guys. I will update when I find something new out.

So I was grading the driveway today and when it started loosing lifting power,i unscrewed the filler cap. No gush of air this time,and no change in operation. So I guess I will be rebuilding this cylinder.